[Mike Shaul]

If you do decide to go with a Frequency to Voltage IC you should also remember that if you are using a source >5v you can possibly create an output voltage >5v which could damage the A/D. You may need to use a buffer/amplifier circuit to clip the output to 5v.

The other issue is that to reduce the ripple you can use higher frequency inputs and smaller capacitors (watch the max input frequency), but as you increase the frequency you also reduce your resolution (larger frequency range in the same number of A/D counts).